Technical Field of the Disclosure
The present embodiment is related in general to anchor handling winches, and in particular to a hybrid winch with torque impulse generation control for anchor handling in offshore semisubmersible oil rigs.
Description of the Related Art
Floating oil rigs are constructed on floating platforms. Some of these platforms are anchored to the sea bed. The floating platforms are tethered to the anchors with cables. One of the most dangerous jobs at sea is anchoring the floating oil rig platforms. These tethering cables are up to three inches in diameter and can be up to three miles long. Anchor handling vessels set the anchors in the sea bed and winch the end of the tethering cable connected to the anchor to create tension on the tethering cable and to set the anchor in the seabed. The anchor handling vessel pulls on the anchor end of the tethering cable to set the anchor.
The anchor handling vessel resists the pull of the tension placed on the anchor cable with the vessel's propulsion system, typically a diesel engine. If the vessel's propulsion system fails, the pull of the anchor cable can pull the vessel underwater and submerge the vessel, risking the lives of the crew aboard the anchor handling vessel. In addition, if the vessel propulsion system fails, tension on the tethering cable can pull the anchor handling vessel backwards without the benefit of steerage, or the benefit of the active resistance of the vessel propulsion system.
Recent advancements in the art disclose a power-assisted winch including a control system for detecting the amount of rotational turning force or torque supplied by a manual input drive to the winch drum, which supplies a rotational turning force or torque from a motor to the winch drum and controls the amount of torque supplied by the motor to the winch drum as a function of the amount of turning force or torque supplied by the manual drive. The function may be a fixed predetermined ratio or it may vary depending upon the level of turning force or torque supplied by the manual input drive. A torque sensor may be utilized to detect the level of manual torque, and a control apparatus will adjust the amount of torque supplied by the motor to the winch drum as required. However, the primary operation of the winch is manual, although it is assisted by power. In the case of semisubmersible oil rigs, manual operation is not feasible due to the heavy duty nature of anchor handling operations.
Floating oil rigs are constructed on floating platforms that are anchored to the sea bed. The floating platforms are tethered to the anchors with cables. One of the most dangerous jobs at sea is anchoring the floating oil rig platforms. These tethering cables are up to 3 inches in diameter and can be up to 3 miles long. Anchoring vessels set the anchors in the sea bed and winch the end of the tethering cable connected to the anchor to create tension on the cable and to set the anchor in the seabed. The anchoring vessel pulls on the anchor end of the tethering cable to set the anchor. The anchoring vessel resists the pull of the tension placed on the anchor cable with the vessel's propulsion system, typically a diesel engine. If the vessel's propulsion system fails, the pull of the anchor cable can submerge the vessel, risking the lives of the crew about the anchoring vessel. In addition, if the vessel propulsion system fails, tension on the tethering cable can pull the anchoring vessel backwards without the benefit steerage in the reverse direction or the benefit of active resistance of the vessel propulsion system.